The present invention concerns the field of power electronics. It relates to a reverse conducting GCT (Gate Commutated Thyristor) in accordance with the preamble of claim 1, and also to an application of such a GCT.
For applications in current source inverters, as are disclosed in U.S. Pat. No. 4,545,002, for example, reverse blocking power semiconductor components such as e.g. thyristors, GTOs or IGCTs (Integrated Gate Commutated Thyristors) are used (with regard to an explanation of the function and the construction of IGCTs, reference is made e.g. to an article by Harold M. Stillman, xe2x80x9cIGCTsxe2x80x94megawatt power switches for medium-voltage applicationsxe2x80x9d, ABB Review 3 (1997)). In this case, it is possible to use both symmetrical components and a series circuit comprising an asymmetrical component and a diode. The problem in application is that a large overvoltage is induced by the commutation inductance during the turn-off into a positive voltage (in the case of GTOs and IGCTs). However, the commutation inductance can only be influenced to a limited extent since it is manifested by leakage inductances.
In the application, therefore, the overvoltage must either be controlled by the semiconductor component used, or be reduced by massive external circuitry. Both approaches lead to losses which limit the performance of the power converter.
It is an object of the invention, therefore, to provide a current source inverter which does not have the abovementioned disadvantages of known current source inverters and, in particular, whose performance is not impaired by the overvoltages produced during turn-off, and also to specify a power semiconductor component for use in such a current source inverter.
The object is achieved by means of the totality of the features of claims 1 and 3. The heart of the invention consists in using, in the bridge paths of the inverter, a power semiconductor component which is avalanche-proof at least under loading in the forward direction. This obviates, in particular, the need for providing additional circuit measures in the inverter. A series circuit comprising a reverse conducting GCT (Gate Commutated Thyristor) and a diode is preferably used.
In the reverse conducting GCT, in which a GCT section and a reverse-connected parallel diode section are integrated beside one another in a semiconductor substrate, the avalanche strength is achieved by virtue of the fact that the diode section is designed in such a way that its avalanche voltage is lower than the blocking voltage of the GCT section.
In accordance with a first preferred refinement of the GCT according to the invention, the diode section comprises, one above the other, a cathode emitter layer, a first base layer, and a first anode emitter layer, and the avalanche voltage or blocking voltage of the diode section is reduced by virtue of the cathode emitter layer being driven in a recessed manner into the semiconductor substrate or the first base layer.
Another preferred refinement is characterized in that the diode section comprises, one above the other, a cathode emitter layer, a first base layer, and a first anode emitter layer, and in that the avalanche voltage or blocking voltage of the diode section is reduced by virtue of the first anode emitter layer being driven in a recessed manner into the semiconductor substrate or the first base layer.
A further refinement of the GCT according to the invention is distinguished by the fact that the diode section comprises, one above the other, a cathode emitter layer, a first base layer, and a first anode emitter layer, and that the avalanche voltage or blocking voltage of the diode section is reduced by virtue of a reduction of the resistivity of the first base layer, the reduction of the resistivity of the first base layer preferably being effected by neutron irradiation.
Finally, it is also possible to effect the avalanche voltage or blocking voltage of the diode section by a reduction in the thickness of the semiconductor substrate in the region of the diode section.
Further embodiments emerge from the dependent claims.